S allius/issue395 (#399)

* add button for languages setting

* build a web module for the dashboard

- load all python module from local dir
- initialize Blueprint and Babel

* set a default key for secure cookies

* add translations to docker container

* improve translation build  

- clean target erases the *.pot
- don't modify the resurt of url_for() calls
- don't translate the language description

* translate connection table, fix icon

* build relative urls for HA ingress

* fix unit test, increase coverage

ha_addons/ha_addon/rootfs/run.sh

@@ -30,4 +30,4 @@ cd /home/proxy || exit
 export VERSION=$(cat /proxy-version.txt)
 
 echo "Start Proxyserver..."
-python3 server.py --json_config=/data/options.json  --log_path=/homeassistant/tsun-proxy/logs/ --config_path=/homeassistant/tsun-proxy/ --log_backups=2
+python3 server.py --rel_urls=True --json_config=/data/options.json  --log_path=/homeassistant/tsun-proxy/logs/ --config_path=/homeassistant/tsun-proxy/ --log_backups=2